Tecobilimat is safe, but it is not effective as a treatment for clade II mpo

News Release

Wednesday, March 12th, 2025

NIH-sponsored trial data provides further evidence to inform MPOX treatment decisions.

The antiviral drug Tecobilimat, used without other antiviral agents, was an international clinical trial sponsored by the National Institutes of Health (NIH) and did not reduce the time to improve clinical resolution of clade II MPOX lesions or pain management in adults. Exam registration was suspended in late 2024 When a provisional analysis showed that Tecobilimat monotherapy was ineffective in the study population. Detailed results were presented at the 2025 conference on retroviruses and opportunistic infections (CROIs) in San Francisco.

“This study took a step towards a better understanding of MPOX disease and potential treatment strategies,” said MD Jeanne Marrazzo, director of MD (NIAID), director of NIH's National Institute of Allergy and Infectious Diseases (NIAID), sponsored and funded the trial. “We appreciate the research team and participants for their contributions to groundbreaking research on diseases that we still don't know enough.”

MPOX It is caused mainly by viruses spread through close contact. Two types of viruses have been identified, called clades I and II. The clade II virus subtype will cause the global MPOX outbreak in 2022, and the virus will continue to circulate at low levels. In 2024, the Clade I outbreak in central and East African countries was declared a public health emergency of international concern. Travel-related cases of clade I MPOX have been reported in the US, but the risk of clade I MPOX to the US population remains low. People whose immune system or certain preexisting skin conditions are significantly affected, children and pregnant women, are at increased risk of developing severe MPOX.

Research into MPOX (STOMP)'s Tecobilitamat began in September 2022 as part of a US government-wide response to the outbreak of Clade II MPOX. There are no US approved MPOX treatments. Based on animal studies, Tecobilimat, also known as Tpoxx, was approved by the Food and Drug Administration (FDA) to treat smallpox– Diseases caused by viruses closely associated with diseases that are far more serious than those that cause MPOX. The drug was not studied in people at MPOX until the suspension trial in the Democratic Republic of the Congo and the complementary research known as the complementary study. palm007 Reported survey results In 2024, it was similar to the findings reported by Stomp.

Stomp was a randomized international efficacy study that enrolled participants who became ill with MPOX for less than 14 days in the US, including Argentina, Brazil, Japan, Mexico, Peru, Thailand and Puerto Rico. Randomized study participants and trial investigators were blinded and therefore were not known who received the Tecobilimat or placebo. This means that pregnant women, participants with a specific skin condition or a substantially suppressed immune system, and participants with severe MPOX disease defined in the study protocol are not randomized. The Stomp study assessed drug safety among all study participants and assessed whether the 14-day course of the tecobilimat single agent in the randomized arm reduced the time to clinical resolution of visible MPOX lesions compared to placebo, improving other outcome measures such as pain.

Randomized participants reported experiencing MPOX symptoms of a Median There was a median of nine MPOX lesions 8 days prior to study invasion. Approximately one-third of participants reported severe pain, selecting scores between 7 and 10 on the 11-point scale. By day 29 after the study invasion, an estimated 83% of participants who received the Tecobilimat had reached clinical resolution, while 84% who received the placebo had a non-significant difference. Among those reporting severe pain at baseline, improvements were similar among those who received Tecobilia mat and placebo, with mean pain reduced by 3.2 points for participants who received Tecobilia mat and 3.1 points for those who received the placebo. Participant lesions were wiped off and tested for the presence of DNA from the virus causing MPOX throughout the study. On day 8, 48% of participants receiving Tecobilimat had undetectable viral DNA compared to 37% of participants receiving placebo. As MPOX resolved, the difference between the two arms was narrowed down by day 15 (82% of those receiving Tecobilimat vs. 80% of those receiving Placebo). These differences were not statistically significant at either time point. Adverse event rates were similar in both randomized study groups.

Individual exploratory analysis of data collected in the open label group of Stomp before the study was concluded was aimed at determining whether factors associated with faster resolution of MPOX lesions in participants at risk or elevated risk of severe MPOX. Faster clinical resolution was observed in participants who were younger, had no HIV, or who lived with HIV but were virally suppressed with antiretroviral therapy. However, there was no association when considering the duration of symptoms prior to study invasion. Investigators noted that although open-label participants in Stomp had fewer lesions, they had slower clinical resolution than reported from the PALM007 trial.

“Since the initiation of Clade II, clinicians treating MPOX have limited evidence to guide their practice, and Stomp has provided the definitive answer to the lack of clinical utility of tecobilimat monotherapy in the randomized populations studied.” “To sum up, these latest results highlight that we have not yet separated which factors affect MPOX disease progression and clinical resolution.”

The Stomp study was conducted by NIH-funded ACTG, a global clinical trial network focusing on HIV and other infectious diseases. Siga Technologies, Inc, based in New York. provided a tecobilimat for this study. The research results will also be published in scientific journals.

For more information about Stomp, please use the identifier to visit ClinicalTrials.gov NCT0534984.

NIAID conducts and supports research across the United States and around the world to study the causes of infectious and immune-mediated diseases and develop better means to prevent, diagnose and treat these diseases. News releases, fact sheets and other NIAID-related materials are Niaid Website.

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